ORIGINAL ARTICLE

Geochemical characteristics and families of the Paleozoic oilseepage and solid bitumen in the Southern Guizhou Depression,SW China

Ningxi Li • Guangli Wang • Bo Gao •

Xianqing Li • Shengbao Shi • Tieguan Wang

Received: 6 December 2013 / Revised: 23 December 2013 / Accepted: 24 February 2014 / Published online: 30 December 2014

� Science Press, Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg 2014

Abstract Fifteen oil seepage and solid bitumen samples

in the Southern Guizhou Depression were analyzed with

GC–MS. Characteristics of molecular markers and carbon

isotopes are discussed systemically. The results showed

that the oil seepage and solid bitumen samples in the

Southern Guizhou Depression could be divided into two

families: Ordovician and Siluric samples, and Permian

samples. The two families are different in alkanes distri-

bution, biomarkers, aromatic hydrocarbon composition,

and stable carbon isotopes; differences mainly caused by

source rock variation.

Keywords Solid bitumen � Oil families � Fossil reservoir

1 Introduction

From the 1950s, Lower Paleozoic fossil and remnant reservoirs

were found in the Southern Guizhou Depression and its

peripheral area in the southeast of Guizhou province (Fig. 1).

Superficial drilling proved that Ordovician and Silurian strata

contained oil and gas in upper composite anticlines. In the 1970s,

the ‘‘number 8’’ geological reconnaissance team discovered the

Majiang fossil reservoir and Kaili remnant reservoir in which

remained 3.53 9 108 t of residual bitumen; they estimated ori-

ginal reserves were 16 9 108 t (Han and Wang 1983).

As a part of the Yangtze platform, the Southern Guizhou

Depression and its peripheral area are similar to other parts of

China in terms of sedimentation, structure, generation, and

accumulation which have combined to make the region a

favorable area to discover large and medium oil and gas fields.

Analysis of the fossil and remnant reservoirs could direct the

exploration of marine carbonate strata in Southern China.

Previous studies have not reached consensus on oil sources

and stages of accumulation (Ma et al. 2004; Zhang et al. 2007;

Gao and Liu 2008; Tenger Qin and Zheng 2008). In this paper,

geochemical characteristics of the Paleozoic oil seepage and

solid bitumen in the Majiang and Kaili areas are analyzed in

detail, and oil–oil correlation and families are discussed. Four

oil seepage samples and eleven solid bitumen samples of the

Southern Guizhou Depression were collected and analyzed by

GC–MS; molecular markers of samples are correlated elab-

orately. According to the oil-correlation, geochemical alter-

ations via generation, migration, and accumulation of crude

oil are recognized which could help analyze oil sources and

direct exploration deployment.

2 Methods

2.1 Geological background

The Majiang fossil reservoir and Kaili remnant reservoir are

both in known petroleum systems which have integrated

N. Li � G. Wang � S. Shi � T. Wang

State Key Laboratory of Petroleum Resources and Prospecting,

and Department of Organic Geochemistry and Environmental

Science, College of Geosciences, China University of Petroleum,

Beijing 102249, China

N. Li (&)

School of Energy Resources, China University of Geosciences,

Beijing 100083, China

e-mail: liningxi@139.com

B. Gao

Exploration and Development Research Institute, Sinopec,

Beijing 10083, China

X. Li

China University of Mining & Technology, Beijing 10083,

China

123

Chin. J. Geochem. (2015) 34(1):85–92

DOI 10.1007/s11631-014-0023-5

source rock, reservoir, cap rock, and overlying strata (Fig. 2).

The fossil reservoir and remnant reservoir are located in the

east of the Southern Guizhou Depression (Fig. 3). The sedi-

mentary characters are complex and include typical platform

facies and basin facies with transitional slope facies. There are

several vertical groups of petroleum systems caused by tec-

tonic activity. The petroleum system of the Majiang fossil

reservoir is sourced from the Lower Cambrian basin facies

mudstone, held in Lower Ordovician and Silurian Wengxiang

Group platform facies reservoirs, and sealed by the Silurian

fourth member of the Wengxiang Group shore facies mud-

stone. Different from Majiang, the petroleum system of the

Kaili remnant reservoir is sourced from the first member of the

Wengxiang Group foreshore facies mudstone, held in the

second and third members of the Wengxiang Group shore

facies sandstone, and sealed by the fourth member of the

Wengxiang Group mudstone. The structure of the oil trap in

the southeastern Guizhou province formed by Duyun move-

ment and Guangxi movement in the Caledonian orogeny,

altered and damaged by Yanshan movement and Sichuan

movement in the early Himalayan period (Han and Wang

1983; Zhang et al. 2007; Gao and Liu 2008; Xiang et al. 2008).

Eight Paleozoic sections of the Majiang and Kaili areas

were observed, and fifteen oil seepage and solid bitumen

samples were collected (Fig. 3). The sample from the Kaili

H47 well is light oil; the Kaili Lushan Ordovician oil

seepage is in limestone geode and Permian oil seepage

occurrence is leaching. The samples were crushed,

extracted, and separated into four fractions (saturated

hydrocarbon, aromatic hydrocarbon, non-hydrocarbon, and

asphaltene). Saturated and aromatic hydrocarbon GC–MS

and isotope analysis were performed.

2.2 Method

Analysis of saturated and aromatic hydrocarbon GC–MS was

conducted using Agilent 6890 gas chromatograph coupled

with 5975i mass spectrometry, equipped with HP-5MS silica

capillary column (standard is GB/T18606-2001). GC condi-

tions: carrier gas is helium with a concentration of 99.999 %;

the temperature of the injection port and transfer line is 300 �C

with a heating program that consists of holding at 80 �C for

1 min, heating up to 310 �C at a rate of 3 �C per minute, and

holding for 16 min. MS conditions: electron impact mode is

Fig. 1 Location of the Southern

Guizhou Depression

86 Chin. J. Geochem. (2015) 34(1):85–92

123

70 eV; filament current flow is 300 lA, and multiplier voltage

is 1,200 V, full scan.

3 Results

3.1 Gross compositions

Saturated and aromatic hydrocarbons comprise the major-

ity in oil seepage samples. The ratio of saturated hydro-

carbon to aromatic hydrocarbon (S/A) of the Kaili Lushan

Permian oil seepage is low at 0.75; three other oil seepage

samples have ratios of 2 to 3. Solid bitumen’s major

fractions are non-hydrocarbon and asphaltene; the S/A

ratio of solid bitumen in the Kaili and Majiang areas is low.

The Majiang Ordovician and Lushan Silurian solid bitu-

men are rich in saturated and aromatic hydrocarbon frac-

tions, in contrast to other bitumen samples. The asphaltene

fraction of Duyun Devonian solid bitumen is high at

94.49 % (Table 1).

In general, oil seepages are rich in saturated and aro-

matic hydrocarbon fractions in comparison to solid bitu-

men samples (the Majiang Ordovician and Lushan Silurian

samples are exceptions). The S/A ratios of upper Paleozoic

samples are low at 0.24 to 0.75; lower Paleozoic samples

from the Majiang area are high at 5.13 to 18.

3.2 Saturated hydrocarbons

3.2.1 n-Alkanes and acyclic isoprenoids

As the most abundant of saturated hydrocarbon, n-alkanes

provide key information about geochemical character

which provides insight into organic matter types, sedi-

mentary environment, thermal evolution stage, and bio-

degradation (Tissot and Welte 1984; Zhang et al. 2005;

Yang et al. 2006).

C13–C24 alkanes dominate oil seepage and solid bitumen

samples, although alkanes range from C11 to C36 with a

single peak. On average the C21-/C22

? ratio in the Majiang

area is 2.88, higher than the Kaili area with a ratio of 1.79.

CPI and OEP values are all around at 1.0 which indicates

for mature stage (Table 2).

The concentration of isoprenoid alkanes is second to

n-alkanes in crude oil. Pr/Ph, Ph/nC18, and Pr/nC17 could

indicate organic facies and maturity (Mei and Liu 1980;

Peters and Moldowan 1993). The values of Pr/Ph in the

southern Guizhou Depression are distributed from 0.62 to

1.44, with an average of 1.13 in the Duyun area, which

displays higher ratios than the Majiang and Kaili areas. Ph/

nC18 and Pr/nC17 exhibit the typical character of marine

crude oil (Fig. 4).

The correlation plate of Pr/Ph and DBT/PH built by

Hughes could provide information about the lithology and

sedimentary environment (Hughes et al. 1995). DBT/PH

values of Permian samples in the Kaili Lushan and Mjiang

areas are greater than 2, and the lower Paleozoic samples

are less than 1 (Fig. 5).

3.2.2 Steranes

C27 regular sterane is from plankton; C29 regular sterane is

from phytoplankton and higher plants. C27, C28, and C29

regular sterane distribution could reflect sources of sedi-

mentary organic matter which is significant to the study of

oil source, so the composition of sterane series is utilized to

divide samples by genetic type (Peters and Moldowan

1993).

The relative content of C27 regular sterane is 13 %–

69 %, PH-1 is too low and is caused primarily by sec-

ondary alterations and not by a different source (Fig. 6).

The Permian samples in the Lushan area are low, in con-

trast to the lower Paleozoic samples. Distinct oil source is

Fig. 2 Stratigraphy and group of source-reservoir-seal in the South-

ern Guizhou Depression

Chin. J. Geochem. (2015) 34(1):85–92 87

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Table 1 Fractions composition of samples

Area Location Samples Layer Saturated hydrocarbon Aromatic hydrocarbon Non-hydrocarbon asphaltene S/A Type

Kaili Lushan LS-O-1 O1h 48.39 23.12 13.44 15.05 2.09 Oil

LS-O-2 P1 28.79 38.52 15.18 17.51 0.75 Oil

LS-B-1 O1h 39.00 20.50 26.50 14.00 1.90 Bitumen

LS-B-2 P1 10.31 43.18 15.60 30.91 0.24 Bitumen

Wanchao LS-B-3 S1–2w1 50.00 21.69 24.40 3.91 2.31 Bitumen

LS-B-4 S1–2w2 31.43 8.57 40.00 20.00 3.67 Bitumen

Panghai PH-1 S1–2w1 54.04 28.42 14.74 2.80 1.90 Oil

Hu47well H47 O1d 61.70 19.30 9.94 9.06 3.20 Oil

Majiang NR 320 MJ-B-1 P2w 7.65 25.14 19.13 48.08 0.30 Bitumen

NR 320 MJ-B-2 S1–2w 42.86 2.38 26.19 28.57 18.00 Bitumen

NR 320 MJ-B-3 O1h 62.85 12.25 12.05 12.85 5.13 Bitumen

Huaqiao MJ-B-4 [1q 28.95 2.63 28.95 39.47 11.00 Bitumen

Duyun Pojiao DY-B-1 O1h 12.71 24.40 9.28 53.61 0.52 Bitumen

Pojiao DY-B-2 S1–2w 53.53 10.37 30.71 5.39 5.16 Bitumen

Pojiao DY-B-3 D3 1.03 2.67 1.81 94.49 0.39 Bitumen

National Road 320

Fig. 3 Location of Majiang

fossil reservoir, Kaili remnant

reservoir and samples

88 Chin. J. Geochem. (2015) 34(1):85–92

123

the main control factor, and the lower Paleozoic samples’

regular sterane distribution is like an asymmetric ‘‘V’’

(C27 [ C28 \ C29).

3.2.3 Terpanes

Tricyclic terpane and hopane are very important bio-

markers in crude oil. The ratio of C21/C23 tricyclic terpane

and C24 tetracyclic terpane/C26 tricyclic terpane can pro-

vide information about maturity and migration (Huang

et al. 1987). Tricyclic terpane content of collected samples

is high and dominated by C23TT; the C21/C23 tricyclic

terpane ratio is less than 1. The C24 tetracyclic terpane/C26

tricyclic terpane ratio of the Lushan Permian samples is

greater than others (Fig. 7).

C3017a(H)-diahopane in crude oil is considered to be

derived from hop-17(21)-ene intermediates via an allylic

oxidation step at C-15 and C-16, and double bond forma-

tion and rearrangement involving the methyl group at C-14

during diagenesis (Peters and Moldowan 1993; Li et al.

2009). Depositional conditions such as Eh–pH and clay

content have greater C30diaH (Philip and Gilbert 1985;

Wang et al. 2000; Zhao and Zhang 2001). The C30diaH/

C30H ratio of the Kaili Permian oil seepage is greater than

others ([0.5); the greater value indicates a sedimentary

environment of shore shallow lake and swamp facies, with

the greater C30diaH value of Kaili Permian oil seepage

probably caused by a distinct sedimentary environment

(Fig. 8).

3.3 Fluorene series

The aromatic hydrocarbon fraction is a significant com-

ponent in crude oil and provides geochemical information

Fig. 4 Crossplot of ratios Ph/nC18 and Pr/nC17

Fig. 5 Crossplot of ratios Pr/Ph and DBT/PH

Table 2 GC-MS data of samples

Area Location Samples Layer Peak Shape C21-/C22

? CPI OEP Pr/Ph Ph/C18 Pr/C17

Kaili Lushan LS-O-1 O1h 17 Single peak 2.45 1.20 1.02 0.62 0.88 0.59

LS-O-2 P1 18 Single peak 1.22 0.99 1.11 0.66 1.44 1.01

LS-B-1 O1h 17 Single peak 1.72 1.21 1.01 0.91 0.90 0.75

LS-B-2 P1 16 Single peak 1.89 1.05 0.99 0.99 1.08 0.97

Wanchao LS-B-3 S1–2w1 20 Single peak 1.54 1.01 0.98 1.06 0.41 0.42

LS-B-4 S1–2w2 23 Double peak 1.36 1.56 1.00 0.71 1.31 0.93

Panghai PH-1 S1–2w1 15 Single peak 1.61 1.10 1.06 0.65 1.00 0.47

Hu47well H47 O1d 13 Single peak 2.51 1.06 1.00 1.19 0.46 0.44

Majiang NR 320 MJ-B-1 P2w 16 Single peak 3.64 2.64 1.02 1.00 1.05 0.80

NR 320 MJ-B-2 S1–2w 17 Single peak 1.97 – 1.03 0.93 1.25 1.00

NR 320 MJ-B-3 O1h 17 Double peak 2.66 1.1- 1.34 0.63 0.53 0.55

Huaqiao MJ-B-4 [1q 18 Single peak 3.26 – 0.91 0.63 1.57 1.03

Duyun Pojiao DY-B-1 O1h 15 Single peak 9.96 – 0.99 1.44 0.31 0.31

Pojiao DY-B-2 S1–2w 24 Single peak 0.68 1.13 1.02 1.00 1.01 0.79

Pojiao DY-B-3 D3 18 Single peak 16.30 – 0.96 0.94 0.63 0.63

Chin. J. Geochem. (2015) 34(1):85–92 89

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about sedimentary environment, sources, and maturity (Li

and He 2008). Fluorene, dibenzothiophene, and dibenzo-

furan are similar in structure; Lin and Huang found that

dibenzothiophene and dibenzofuran were related to oxi-

dation or deoxidation environments (Lin et al. 1987). In

general, a greater value of dibenzothiophene indicates that

crude oil and source rock formed in a marine saline envi-

ronment with strong deoxidation.

Contents of fluorene less than 30 %, and greater diben-

zothiophene values reflect the deoxidation environment. The

dibenzofuran content of the Kaili Ordovician and Silurian

samples is greater than others with a range of 15 % to 27 %

(Fig. 9).

3.4 Carbon isotope

Hydrocarbons inherit the carbon isotopes of the source

organic matter and are affected by fractionation via thermal

evolution processes. Generally speaking, differences in the

stable carbon isotope (d13C) fraction between samples of

Fig. 7 Crossplot of ratios C21/

C23 tricyclic terpane and C24

tetracyclic terpane/C26 tricyclic

terpane

Fig. 8 Crossplot of ratios Ts/

(Ts?Tm) and C30diaH/C30H

hopanes

Fig. 6 Ternary diagram of C27,

C28 and C29 sterane composition

90 Chin. J. Geochem. (2015) 34(1):85–92

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the same source crude oil affected by thermal evolution

would not be greater than 3 % (Peters and Moldowan

1993; Stahl 1977), whereas d13C differences greater than

3 % imply different oil sources. d13C of the Kaili Permian

oil seepage is -28 %, making it distinct from Ordovician

and Silurian Oil seepage (Fig. 10). Solid bitumen samples

display a similar pattern, except for the Duyun and Kaili

Lushan Ordovician and Silurian samples—a difference that

is caused by variations in maturity (Fig. 11).

4 Discussion

Oil correlation shows that oil seepage and solid bitumen of

the Southern Guizhou Depression can be divided into two

families. One is the Permian samples which have a lower

S/A ratio and a greater ratio of DBT/PH. Lower content of

C27 regular sterane indicates less plankton input. A greater

ratio of C24FT/C26TT and C30diaH/C30H indicates a dis-

tinct sedimentary environment. Greater content of

Fig. 10 Stable carbon isotope

of oil seepage

Fig. 11 Stable carbon isotope

of solid bitumen

Fig. 9 Ternary diagram of

fluorene, dibenzothiophene and

dibenzofuran composition

Chin. J. Geochem. (2015) 34(1):85–92 91

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dibenzothiophene, lower content of dibenzofuran, and

heavier stable isotopes reflect that the Permian samples

have a different source rock from the lower Paleozoic

samples.

The second family is O–S oil seepage and solid bitumen

with a ratio of DBT/PH less than 1, representing charac-

teristic marine facies hydrocarbons. C27–C28–C29 regular

sterane is distributed like an asymmetrical ‘‘V’’, indicating

mainly sources are plankton. The ratio of C21TT/C23TT

less than 1, C24FT/C26TT less than 2, and C30diaH/C30H

less than 0.5 generally indicate an oxygen-poor and low-

clay environment. Richness in dibenzothiophene and

dibenzofuran reflects a reduced environment; stable isotope

are light besides individual samples affected by maturity.

The differences in the geochemical characteristics

between the O–S and P oil seepage and solid bitumen are

caused by different source rocks. O–S samples are gener-

ated from Lower Cambrian source rock and the Permian

samples may be from Lower Permian source rock. CPI and

OEP are balanceable and the maturity of solid bitumen is

higher.

5 Conclusion

The oil seepage and solid bitumen in the Southern Guizhou

Depression can be divided into two families: Permian

samples and lower Paleozoic samples. The two families are

different in alkane distribution, biomarkers, aromatic

hydrocarbon composition, and stable carbon isotopes due

to variations in source rock.

Acknowledgments We thank Dr Jin Zhijun, Dr Liu Dongsheng,

and Zhou Dikang for their help with outcrop investigations; and two

anonymous reviewers for comments and suggestions. This work was

funded by the State Key Project of Petroleum (2008ZX05005-001-

009HZ), the National Natural Science Foundation of China

(41172126), the State Key Laboratory of Petroleum Resources and

Prospecting (PRP2010-01) and the Science Foundation of China

University of Petroleum (LLYJ-2011-05 and KYJJ-2012-01-01).

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